A pump may be defined as a machine or apparatus which imparts energy to a fluid flowing therethrough. All pumps basically fall into one of two categories or types of pumps: positive displacement pumps and dynamic pumps.
Positive displacement pumps embody one or more chambers and operate by forcing a set volume of fluid from the inlet pressure section of the pump into the discharge portion of the pump, i.e., alternating action of filling and emptying the chamber or chambers with the fluid. Representative types of positive displacement pumps include reciprocating pumps such as those having piston/plunger type construction, metering construction and diaphram construction, and rotary pumps such as those having screw rotor type construction and intermeshing gear wheel construction. Reciprocating pumps operate intermittently whereas rotary pump operate continuously.
Dynamic pumps operate by developing a high fluid velocity and converting the velocity into pressure in a diffusing flow passage. Representative types of dynamic pumps include horizontal or vertical centrifugal pumps, axial pumps and turbine pumps.
Centrifugal pumps comprise a wide class of pumps which in their most essential form consist of two basic components. A first component comprises a rotating element, including an impeller mounted on a shaft which is in turn supported by bearings and driven through a flexible or rigid coupling by a driver. A second component comprises a stationary element comprised of a casing, stuffing box and bearings. The casing includes suction and discharge nozzles, supports the bearings, and houses the rotor assembly.
As fluid enters a centrifugal pump, it is forced by atmospheric or other pressure into a set of rotating vanes which constitute an impeller. The impeller imparts tangential acceleration to the fluid and discharges the fluid at a relatively high velocity at its periphery. The velocity of the fluid is then converted into pressure energy or pressure head by means of a volute or by a set of stationary diffuser vanes surrounding the impeller periphery. Pumps having volute casings are generally referred to as volute centrifugal pumps, and pumps having diffuser vanes are generally referred to as diffuser pumps. Since centrifugal pumps have no valves, fluid flow is uniform and free of low-frequency pulsations.
In a closed system such as a centrifugal pump, the principle of conservation of energy states that the total energy input is equal to the total energy output from that system. Bernoulli's equation in its more general form for total mechanical energy balance can be stated as follows: EQU P.sub.1 +Z.sub.1 +V.sub.1 +E.sub.p =P.sub.2 +Z.sub.2 +V.sub.2 +F.sub.L Eq. 1
where
P.sub.1 is pressure energy at the point of entrance,
Z.sub.1 is potential energy at the point of entrance,
V.sub.1 is kinetic energy or velocity head at the point of entrance,
E.sub.p is pump energy,
P.sub.2 is pressure energy at the point of exit,
Z.sub.2 is potential energy at the point of exit,
V.sub.2 is kinetic energy or velocity head at the point of exit, and
F.sub.L is friction loss between the point of entrance and point of exit.
In order to determine the power requirement of a given pump, Bernoulli's equation can be used in the following restated form: EQU E.sub.p =(P.sub.2 -P.sub.1)+(Z.sub.2 -Z.sub.1)+(V.sub.2 -V.sub.1)+F.sub.L Eq. 2
It is readily apparent that if friction loss (F.sub.L) can be reduced within a given pump, the power requirement for that pump will also be reduced, and considerable savings in operation costs can be realized.
Those skilled in the art have long known that if the friction of a fluid flow through the interior of a centrifugal pump were reduced, the savings in terms of reduced power requirement would be substantial. Since most, if not all centrifugal pump casings are cast-metal, the interior surface of the casings contain variations including surface roughness, pits, nicks, gouges, blow holes, or positive metal. All of these variations will substantially impede fluid flow, i.e., result in substantial friction loss.
Up to now, the only means of remedying these surface variations consisted of manual operations including the utilization of files and rotary burr tools, sanding and grinding. These methods, however, are effective largely as corrective measures for gross variations or imperfections. Single cast pump casings present another problem in that the interior surface of the casing is largely inaccessible to manual operations. Even where the interior surface of the casings is accessible, the difficulty of manual operations in terms of control, uniformity and the degree of physical dexterity required renders the finish on the interior surface of a so-called "finished" casing largely untreated. Further, performance of manual operations on the interior surface of a pump casing is a time consuming task and renders the "finished" article quite expensive.
The present practice by industry is to accept the internal surface variations of casings as unavoidable and compensate for the energy loss due to friction by utilizing drivers with increased power output capabilities. The result is a higher cost of operation which is attributable to higher energy requirements and higher maintenance costs due to increased wear and stress on the moving parts of the pump.
The foregoing serves to illustrate the state of the art and the problem addressed and solved by the present invention.
It is an object of the present invention to provide a method of working the interior surface of pump casings to reduce internal fluid flow friction of dynamic pumps.
It is a further object to provide such a method to reduce the internal fluid flow friction of centrifugal volute pumps.
Another object is to provide a method of providing and ensuring a consistent level of minimal internal fluid flow friction of dynamic pumps.
Still another object is to provide a method of providing and ensuring a uniform level of minimal internal fluid flow friction of centrifugal volute pumps.
Yet another object is to provide a method of providing industry with a standard of minimal internal fluid flow friction of dynamic pumps.
Another object is to provide a method of providing industry with a standard of minimal internal friction of centrifugal volute pumps.
A further object is to provide parts and components which have been worked to effect minimal internal fluid flow friction in dynamic pumps.
A further object is to provide parts and components which have been worked to effect minimal internal fluid flow friction in centrifugal volute pumps.